The iron lung, formally known as a tank respirator, is a specialized medical device that provided life support for patients unable to breathe independently. This large, horizontal cylinder was a major breakthrough in artificial respiration, offering continuous life support for individuals with paralyzed breathing muscles. Invented in the late 1920s, it became a symbol of medical intervention during public health crises. It is a classic example of a negative pressure ventilator designed to physically assist the mechanics of the human respiratory system.
The Mechanism of Negative Pressure Ventilation
The iron lung operates on the principle of external negative pressure ventilation (ENPV), mimicking the body’s natural breathing process. A patient is sealed inside the airtight, metal chamber up to their neck, with a rubber collar preventing air leakage. An electric motor connected to a pump or bellows outside the tank rhythmically changes the air pressure within the enclosed space.
When the pump draws air out of the chamber, it creates negative pressure around the patient’s chest and abdomen. This reduction in external pressure forces the chest wall and diaphragm to expand outward, causing the lungs to inflate and pull air in through the patient’s open airway. This mechanical action performs the inhalation phase.
The pump then allows the air pressure inside the tank to return to a normal atmospheric level. This release allows the patient’s chest and lungs to recoil passively, pushing the air back out in the exhalation phase. The continuous cycling between negative and atmospheric pressure provides a steady, controlled rate of breathing for patients whose own muscles are too weak or paralyzed to perform respiration.
The Era of Polio and Mass Use
The iron lung was first developed by Philip Drinker and Louis Agassiz Shaw in 1928, initially for treating victims of coal gas poisoning. However, the device quickly became synonymous with the poliomyelitis epidemics that swept across the world in the mid-20th century. The poliovirus, in its most severe form known as bulbar polio, attacked the nerve cells in the brainstem and spinal cord that controlled the muscles for swallowing and breathing.
Patients with respiratory paralysis, particularly those whose diaphragm and intercostal muscles were affected, required immediate mechanical assistance. The iron lung sustained breathing for weeks or even months, offering the first chance of survival for patients who otherwise would have died from suffocation. At the peak of the epidemic in the United States in 1952, over 57,000 cases were reported, creating unprecedented demand for the tank respirators.
Hospital wards were regularly filled with rows of these large, coffin-like machines; their rhythmic whooshing sound became the constant background noise of the polio era. While some patients only needed the device temporarily until their respiratory muscles recovered, others suffered permanent damage and became lifelong users. By 1959, an estimated 1,200 people in the U.S. relied on the iron lung for their every breath.
Transition to Modern Respiratory Care
The reliance on the iron lung began to decline dramatically following the introduction of the Salk polio vaccine in 1955. The vaccine’s success in preventing the paralytic disease significantly reduced the number of new cases requiring mechanical ventilation. Simultaneously, advancements in medical technology led to the development of alternative, more efficient methods of respiratory support.
Modern ventilators operate using positive pressure ventilation, a fundamentally different approach where air is actively pushed into the patient’s lungs, often through a tube inserted into the airway. This positive pressure system is far more compact and portable than the bulky tank respirator. It also allows medical personnel easier access to the patient’s body for nursing care and medical procedures.
Other non-invasive alternatives, such as bi-level positive airway pressure (BiPAP) devices and smaller, shell-like negative pressure units called cuirass ventilators, have further replaced the need for the full-body iron lung. Despite the near-total obsolescence of the machine, a very small number of polio survivors around the world continue to rely on the old tank respirators, having adapted to the device over decades and finding modern alternatives unsuitable for their specific needs.